CN110426788B - Heatless coarse wavelength division multiplexing device - Google Patents
Heatless coarse wavelength division multiplexing device Download PDFInfo
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- CN110426788B CN110426788B CN201910672781.1A CN201910672781A CN110426788B CN 110426788 B CN110426788 B CN 110426788B CN 201910672781 A CN201910672781 A CN 201910672781A CN 110426788 B CN110426788 B CN 110426788B
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29346—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by wave or beam interference
- G02B6/2935—Mach-Zehnder configuration, i.e. comprising separate splitting and combining means
- G02B6/29352—Mach-Zehnder configuration, i.e. comprising separate splitting and combining means in a light guide
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
- G02B6/2938—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
- G02B6/29398—Temperature insensitivity
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Abstract
The application discloses no hot coarse wavelength division multiplexing device includes the cascaded filter unit of one set or multiunit, and each set of filter unit includes a MZ filter, the MZ filter includes first waveguide arm and second waveguide arm, wherein: the first waveguide arm is provided with a first mode waveguide for transmitting a first mode light wave; the second waveguide arm is provided with a second mode waveguide for transmitting a second mode light wave; the difference value between the optical path of the first mode light wave transmitted through the first mode waveguide and the optical path of the second mode light wave transmitted through the second mode waveguide meets the preset time delay requirement and temperature insensitivity requirement. The thermo-optic coefficient difference of different modes of light waves is utilized to compensate thermo-optic influences of the upper arm and the lower arm with unequal lengths of the MZ filter, so that the influences of temperature on time delay of the two arms are the same, the heatless condition of the coarse wavelength division multiplexing device is met, the influence of the temperature on the central wavelength is fundamentally solved, and the device is simple in process, independent of temperature, small in size and large in tolerance.
Description
Technical Field
The present application relates to, but is not limited to, the technical field of optical communication, and in particular, to an athermal coarse wavelength division multiplexing device.
Background
Wavelength Division Multiplexing (WDM) is a technique to enhance the capacity of data communication links. For WDM, the independent signals are carried by different wavelengths, which spreads the bandwidth over time. In recent years, many WDM devices have been developed on silicon platforms using ultra-high refractive index contrast and mature fabrication techniques for silicon waveguides. However, one of the challenges with silicon WDM devices is wavelength drift due to thermal sensitivity or non-uniformity in silicon waveguide fabrication. Therefore, wavelength tuning and tuning are required to ensure wavelength alignment, which may result in increased cost and power consumption. Coarse Wavelength Division Multiplexing (CWDM) techniques with 20nm channel spacing have been proposed in optical communication networks, which relax the accuracy of the laser Wavelength and the external temperature variation. Such CWDM techniques have been applied to devices on silicon platforms to relax the requirements for precise thermal control and stringent manufacturing processes, thereby reducing cost and power consumption.
Athermal and flat-top transmission are two major requirements of silicon WDM devices. Currently, passband planarization is effectively achieved by using cascaded ring resonators, Arrayed multi-mode Interference (MMI) assisted Aperture Waveguide Gratings (AWGs), Mach-Zehnder (MZ) filter multi-stage Interference, and a combination of Direct Coupler (DC) DC and MZ. However, silicon materials have a large thermo-optic coefficient, the refractive index of silicon is sensitive to changes in ambient temperature, and the temperature range of industrial-grade module environmental problems is 233K to 358K. The bulk silicon thermo-optic coefficient is 1.94e-4 at a temperature of 1.3um wavelength 295K. This causes the equivalent refractive index of the mode to change with changes in ambient temperature, which in turn has a significant impact on the performance of the CWDM device.
For athermal CWDM devices, the reported solutions are: integrating silicon with negative thermo-optic materials (such as titanium dioxide TiO2 and the like); thermal tuning; cascading multiple waveguides, etc. The solutions all take the increase of the flatness of the pass band as a starting point to reduce the influence of temperature drift on the device performance, and actually do not solve the problem of wavelength drift caused by temperature; in addition, the schemes have the defects of difficult realization of mass production, large device size, complex process, high cost and the like. Therefore, it is urgent to design a new CWDM device with simple process, temperature independence, small size and large tolerance.
Disclosure of Invention
The application provides a no hot coarse wavelength division multiplexing device, can fundamentally solve the influence of temperature to central wavelength, and simple process, temperature are irrelevant, the size is little, the tolerance is big.
The application provides an athermal coarse wavelength division multiplexing device, includes one set or multiunit cascaded filter unit, every set of filter unit includes a Mach-Zehnder MZ filter, MZ filter includes first waveguide arm and second waveguide arm, wherein:
the first waveguide arm is provided with a first mode waveguide for transmitting a first mode light wave; the second waveguide arm is provided with a second mode waveguide for transmitting a second mode light wave;
the difference value between the optical path of the first mode light wave transmitted through the first mode waveguide and the optical path of the second mode light wave transmitted through the second mode waveguide meets the preset time delay requirement and temperature insensitivity requirement.
In an exemplary embodiment, each group of filtering units further includes an optical splitter and an optical combiner, where:
the input end of the optical splitter is connected with the input end of the athermal coarse wavelength division multiplexing device or the output end of the first waveguide arm and the output end of the second waveguide arm of the previous-stage filtering unit, and the output end of the optical splitter is respectively connected with the input end of the first waveguide arm and the input end of the second waveguide arm;
the input end of the optical combiner is respectively connected with the output end of the first waveguide arm and the output end of the second waveguide arm, and the output end of the optical combiner is used as the input end of the first waveguide arm and the input end of the second waveguide arm which are connected with a next-stage filtering unit, or is used as the output end of the athermal coarse wavelength division multiplexing device.
In one exemplary embodiment, the optical splitter is a directional coupler or a Y-splitter; the light combiner is a directional coupler or a Y-type light splitter.
In an exemplary embodiment, the first mode is the TE0 mode and the second mode is the TE1 mode;
the first waveguide arm and the second waveguide arm are respectively provided with two mode converters, wherein one mode converter is a first mode converter of a TE0 mode to a TE1 mode, and the other mode converter is a second mode converter of a TE1 mode to a TE0 mode.
In an exemplary embodiment, the waveguide width of the first mode waveguide is a first waveguide width, the waveguide width of the second mode waveguide is a second waveguide width, and the first waveguide width is not equal to the second waveguide width.
In one exemplary embodiment, the first waveguide width is 1000 nanometers and the second waveguide width is 600 nanometers.
In an exemplary embodiment, the first waveguide arm and the second waveguide arm are respectively provided with two waveguide converters.
In an exemplary embodiment, the preset delay requirement is:
(nTE1(λ)·LTE1-nTE0(λ)·LTE0)·k0-m·2π＝delay(λ)；
the preset temperature insensitivity requirement is as follows:
(ΔnTE1(λ)·LTE1-ΔnTE0(λ)·LTE0)·k0＝0；
where λ is the wavelength in the medium, nTE1(λ) is the effective refractive index of the TE1 mode, LTE1Length of TE1 mode walk, nTE0(λ) is the effective refractive index of the TE0 mode, LTE0The length of TE0 mode, m is the interference order, delay (λ) is the time delay corresponding to wavelength λ, Δ nTE1(λ) is the effective refractive index change, Δ n, of the TE1 mode at different temperaturesTE0(λ) is the effective index change, k, of the TE0 mode at different temperatures0Is the wave vector in vacuum, k0＝2π/λ0，λ0Is the wavelength of light in vacuum.
In contrast to the related art, an athermal coarse wavelength division multiplexing device of the present application is provided, in which a first mode waveguide for transmitting a first mode light wave is disposed on one waveguide arm of an MZ filter, a second mode waveguide for transmitting a second mode light wave is disposed on the other waveguide arm, the difference value of the optical path of the first mode light wave transmitted through the first mode waveguide and the optical path of the second mode light wave transmitted through the second mode waveguide meets the preset time delay requirement and temperature insensitivity requirement, the thermo-optic coefficient difference of different mode light waves is utilized to compensate the thermo-optic influence of the upper arm and the lower arm with different lengths of the MZ filter, so that the influence of the temperature on the time delay of the two arms is the same, therefore, the athermal condition of the coarse wavelength division multiplexing device is met, the influence of temperature on the center wavelength is fundamentally solved, and the device has the obvious advantages of simple process, irrelevant temperature, small size, large tolerance and the like.
Drawings
The accompanying drawings are included to provide an understanding of the present disclosure and are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the examples serve to explain the principles of the disclosure and not to limit the disclosure.
FIG. 1 is a schematic diagram of a MZ single-stage structure in a conventional CWDM device;
fig. 2 is a schematic structural diagram of a single-stage filter unit of a heatless CWDM device according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a single-stage filter unit of an athermal CWDM device according to an embodiment of the present invention;
FIG. 4 is a graph showing the variation of thermo-optic coefficients of the TE0 mode, the TE1 mode and the TM0 mode with the waveguide width according to the embodiment of the present invention;
FIG. 5 is a schematic diagram of a symmetrical layout of an MZ single-stage structure in an athermal CWDM device in accordance with an embodiment of the present invention;
fig. 6 is a schematic structural diagram of an MZ cascade-based athermal CWDM device according to an embodiment of the present invention;
fig. 7 is a schematic diagram of a 4-channel wavelength division multiplexing implementation by cascading athermal CWDM devices according to an embodiment of the present invention.
Detailed Description
The present application describes embodiments, but the description is illustrative rather than limiting and it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the embodiments described herein. Although many possible combinations of features are shown in the drawings and discussed in the detailed description, many other combinations of the disclosed features are possible. Any feature or element of any embodiment may be used in combination with or instead of any other feature or element in any other embodiment, unless expressly limited otherwise.
The present application includes and contemplates combinations of features and elements known to those of ordinary skill in the art. The embodiments, features and elements disclosed in this application may also be combined with any conventional features or elements to form a unique inventive concept as defined by the claims. Any feature or element of any embodiment may also be combined with features or elements from other inventive aspects to form yet another unique inventive aspect, as defined by the claims. Thus, it should be understood that any of the features shown and/or discussed in this application may be implemented alone or in any suitable combination. Accordingly, the embodiments are not limited except as by the appended claims and their equivalents. Furthermore, various modifications and changes may be made within the scope of the appended claims.
Further, in describing representative embodiments, the specification may have presented the method and/or process as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. Other orders of steps are possible as will be understood by those of ordinary skill in the art. Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. Further, the claims directed to the method and/or process should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the embodiments of the present application.
Fig. 1 is a schematic diagram of a MZ single-stage structure in a conventional CWDM device. Due to the length difference delta L of the upper arm and the lower arm of the MZ, the upper waveguide and the lower waveguide are asymmetric, the influence of temperature on propagation delay is also asymmetric, the delay difference of the MZ depends on the change of the temperature, and the temperature drift phenomenon of the CWDM spectrum occurs.
As shown in fig. 2, an embodiment of the present invention provides an athermal coarse wavelength division multiplexing device, including one or more cascaded sets of filtering units, each set of filtering unit including an MZ filter, where the MZ filter includes a first waveguide arm and a second waveguide arm, where:
the first waveguide arm is provided with a first mode waveguide for transmitting a first mode light wave; the second waveguide arm is provided with a second mode waveguide for transmitting a second mode light wave;
the difference value between the optical path of the first mode light wave transmitted through the first mode waveguide and the optical path of the second mode light wave transmitted through the second mode waveguide meets the preset time delay requirement and temperature insensitivity requirement.
In an exemplary embodiment, each group of filtering units further includes an optical splitter and an optical combiner, where:
the input end of the optical splitter is connected with the input end of the athermal coarse wavelength division multiplexing device or the output end of the first waveguide arm and the output end of the second waveguide arm of the previous-stage filtering unit, and the output end of the optical splitter is respectively connected with the input end of the first waveguide arm and the input end of the second waveguide arm;
the input end of the optical combiner is respectively connected with the output end of the first waveguide arm and the output end of the second waveguide arm, and the output end of the optical combiner is used as the input end of the first waveguide arm and the input end of the second waveguide arm which are connected with a next-stage filtering unit, or is used as the output end of the athermal coarse wavelength division multiplexing device.
In an example of this embodiment, the optical splitter is a directional coupler or a Y-splitter; the light combiner is a directional coupler or a Y-type light splitter. The optical splitters and optical combiners are devices having a specific coupling ratio or splitting ratio (the specific coupling ratio or splitting ratio is determined in the design of the CWDM device).
In an exemplary embodiment, the first mode is the TE0 mode and the second mode is the TE1 mode;
the first waveguide arm and the second waveguide arm are respectively provided with two mode converters, wherein one mode converter is a first mode converter of a TE0 mode to a TE1 mode, and the other mode converter is a second mode converter of a TE1 mode to a TE0 mode.
The two mode converters are respectively arranged on the first waveguide arm and the second waveguide arm, so that the structural symmetry of the two waveguide arms is ensured.
In an exemplary embodiment, the waveguide width of the first mode waveguide is a first waveguide width, the waveguide width of the second mode waveguide is a second waveguide width, and the first waveguide width is not equal to the second waveguide width.
In one example of this embodiment, the first waveguide width is 1000 nanometers (nm) and the second waveguide width is 600 nm.
In an exemplary embodiment, the first waveguide arm and the second waveguide arm are respectively provided with two waveguide converters.
In an exemplary embodiment, the preset delay requirement is:
(nTE1(λ)·LTE1-nTE0(λ)·LTE0)·k0-m·2π＝delay(λ)；
the preset temperature insensitivity requirement is as follows:
(ΔnTE1(λ)·LTE1-ΔnTE0(λ)·LTE0)·k0＝0；
where λ is the wavelength in the medium, nTE1(λ) is the effective refractive index of the TE1 mode, LTE1Length of TE1 mode walk, nTE0(λ) is the effective refractive index of the TE0 mode, LTE0The length of TE0 mode, m is the interference order, delay (λ) is the time delay corresponding to wavelength λ, Δ nTE1(λ) is the effective refractive index change, Δ n, of the TE1 mode at different temperaturesTE0(λ) is the effective index change, k, of the TE0 mode at different temperatures0Is the wave vector in vacuum, k0＝2π/λ0，λ0Is the wavelength of light in vacuum.
As shown in fig. 3, an embodiment of the present invention provides a heatless CWDM device, which is formed by cascading a plurality of sets of DC and MZ delay lines, and compensates the thermal-optical influences of the upper and lower arms with different lengths by changing the thermal-optical coefficients of the upper and lower MZ waveguides, i.e., using the difference of the thermal-optical coefficients of different modes in the waveguides with different widths, so that the temperature has the same influence on the time delays of the two arms, thereby satisfying the heatless condition; the two arms of the MZ meeting the non-thermal condition still have time delay difference, and the time delay difference meets the design requirement of the CWDM by adjusting the length of the two arms in multiples.
The application compensates the thermo-optic influence of upper and lower arms with unequal length by changing the thermo-optic coefficients of the upper and lower waveguides of the MZ, namely utilizing the difference of the thermo-optic coefficients of different modes in the waveguides with different widths, so that the influence of temperature on the time delay of the two arms is the same, and the time delay requirement and the temperature insensitive design of the MZ can be simultaneously met in a shorter length range, namely the following two equations are met:
(nTE1(λ)·LTE1-nTE0(λ)·LTE0)·k0-m · 2 pi ═ delay (λ) meets the CWDM arm length delay requirement;
(ΔnTE1(λ)·LTE1-ΔnTE0(λ)·LTE0)·k00 satisfies the athermal design;
wherein: n isTE1(λ) is the effective refractive index of the TE1 mode, LTE1Length of TE1 mode walk, nTE0(λ) is the effective refractive index of the TE0 mode, LTE0Length traversed by TE0 mode, k0Is the wave vector in vacuum, and m is the interference order. The delay (λ) has been determined in the design of CWDM devices by fitting the values of LTE1 and LTE2 to m, so that the two equations have the smallest possible deviation over the entire wavelength range.
Generally, the larger the difference between the thermo-optic coefficients of the two arms is, the larger the difference between the lengths of the two arms is, so that the shorter MZ arm length can meet the requirement of the CWDM on the time delay difference. As shown in fig. 4, different waveguide widths correspond to different thermo-optic coefficients in different modes, the thermo-optic coefficient in the same mode changes flatly, and the representative width tolerance is large, so that the thermo-optic coefficient difference based on different modes can meet the requirement of large width tolerance.
Fig. 5 is a symmetrical layout diagram of an MZ single-stage structure in a CWDM device according to an embodiment of the present invention. As shown in FIG. 5, the upper and lower arms of the MZ are symmetrical in structure, and the process uniformity is good. The application compensates the thermo-optic influence of the upper arm and the lower arm with unequal lengths by changing the thermo-optic coefficients of the upper waveguide and the lower waveguide of the MZ, namely, by utilizing the difference of the thermo-optic coefficients of different modes in the waveguides with different widths, so that the influence of the temperature on the time delay of the two arms is the same, and the condition of no heat is met. The phase compensation device is based on the same material and different waveguide structures, has different modes of thermo-optic coefficient difference, achieves a phase compensation function, does not introduce other devices, and is small in size. Compared with other CWDM devices, the temperature-sensitive CWDM device has the advantages of fundamentally solving the influence of temperature on the center wavelength, along with simple process, irrelevant temperature, small size, large tolerance and the like.
Fig. 6 is a schematic structural diagram of an MZ cascade-based athermal CWDM device according to an embodiment of the present invention. The athermal CWDM device consists of 5 DCs with different coupling coefficients and 4 MZs with different length differences. The role of DC is to distribute the optical power and by designing a specific coupling ratio, a flat output spectrum is achieved. The MZ can select the wavelength needing to be output by the design of different length differences of the upper arm and the lower arm. According to the results of the thermo-optic coefficient variation with width of the TE0 and TE1, the TE0 of the 1000nm width waveguide and the TE1 of the 600nm width waveguide can meet the requirements of larger thermo-optic coefficient difference and waveguide width tolerance. Therefore, the thermo-optic compensation is completed by selecting the thermo-optic coefficient difference between the TE0 mode of the 1000nm wide waveguide and the TE1 mode of the 600nm wide waveguide. Performing thermo-optical compensation in this way requires introducing a TE0- >600nm waveguide TE1 mode converter and a 420nm waveguide TE0- >1000nm waveguide TE0 band converter (Taper) on both arms of the MZ. In order to ensure the structural symmetry of the upper and lower arms, the MZ is laid out as shown in FIG. 4. The present embodiment is based on O-band (1310nm) heatless CWDM design, but the design principle is also applicable to other bands, such as C-band (1550nm), L-band (1600nm), etc.
The working mode is as follows: firstly, input light containing four wavelengths of λ 1, λ 2, λ 3 and λ 4 is input from a DC1 port, power distribution is performed by a DC1, the input light is divided into 2 paths to a MZ1, the two optical signals generate specific phase differences after passing through different paths, specific wavelengths are output from different ports, enter a DC2, an MZ2 and reach a DC5 according to the same working principle, and finally specific wavelengths are output from a straight (through) end and a cross (cross) end of a DC5 respectively, so that a filtering function is completed.
In this embodiment, the waveguide of the whole CWDM device is made of silicon, the cladding is made of silicon oxide, the height of the waveguide is 220nm, and the width of the waveguide is 420nm, 600nm, or 1000nm according to design. The DC pitch (Gap) was 250nm and the curved waveguide used a bezier bend with a radius of 3 microns (μm). The structures referred to in this application are the mode converter TE0 to TE1, and two waveguide width conversion Taper (including 420nm- >600nmTaper and 420nm- >1000 nmTaper). The athermal CWDM device shown in fig. 6 requires a total of 8 pairs of mode conversion devices.
Fig. 7 is a schematic diagram of a 4-channel wavelength division multiplexing structure implemented by two-stage cascade of the athermal CWDM device according to the present application, which is composed of A, B, C athermal CWDM devices, and implements the 4-channel wavelength division multiplexing function in a single-stage two-step manner. To reduce complexity, the DC parameters of the athermal CWDM device A, B, C are consistent; B. the length difference deltal between the upper arm and the lower arm of C is half of the length difference between the upper arm and the lower arm of a, and in order to meet the requirements of B, C straight ends and cross ends, the phase needs to be slightly adjusted. Compared with other cascaded CWDM devices, the center wavelength of the output spectral line of the heatless CWDM device is more accurate after the cascaded device is cascaded.
It will be understood by those of ordinary skill in the art that all or some of the steps of the methods, systems, functional modules/units in the devices disclosed above may be implemented as software, firmware, hardware, and suitable combinations thereof. In a hardware implementation, the division between functional modules/units mentioned in the above description does not necessarily correspond to the division of physical components; for example, one physical component may have multiple functions, or one function or step may be performed by several physical components in cooperation. Some or all of the components may be implemented as software executed by a processor, such as a digital signal processor or microprocessor, or as hardware, or as an integrated circuit, such as an application specific integrated circuit. Such software may be distributed on computer readable media, which may include computer storage media (or non-transitory media) and communication media (or transitory media). The term computer storage media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data, as is well known to those of ordinary skill in the art. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, Digital Versatile Disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can accessed by a computer. In addition, communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media as known to those skilled in the art.
Claims (7)
1. An athermal coarse wavelength division multiplexing device comprising one or more cascaded sets of filtering units, each set of said filtering units comprising a mach-zehnder filter comprising a first waveguide arm and a second waveguide arm, wherein:
the first waveguide arm is provided with a first mode waveguide for transmitting a first mode light wave; the second waveguide arm is provided with a second mode waveguide for transmitting a second mode light wave;
the difference value between the optical path of the first mode light wave transmitted through the first mode waveguide and the optical path of the second mode light wave transmitted through the second mode waveguide meets the preset time delay requirement and temperature insensitivity requirement;
wherein the first mode is a TE0 mode, and the second mode is a TE1 mode;
the first waveguide arm and the second waveguide arm are respectively provided with two mode converters, wherein one mode converter is a first mode converter of a TE0 mode to a TE1 mode, and the other mode converter is a second mode converter of a TE1 mode to a TE0 mode.
2. The athermal coarse wavelength division multiplexing device of claim 1, wherein each set of filtering units further comprises an optical splitter and an optical combiner, wherein:
the input end of the optical splitter is connected with the input end of the athermal coarse wavelength division multiplexing device or the output end of the first waveguide arm and the output end of the second waveguide arm of the previous-stage filtering unit, and the output end of the optical splitter is respectively connected with the input end of the first waveguide arm and the input end of the second waveguide arm;
the input end of the optical combiner is respectively connected with the output end of the first waveguide arm and the output end of the second waveguide arm, and the output end of the optical combiner is used as the input end of the first waveguide arm and the input end of the second waveguide arm which are connected with a next-stage filtering unit, or is used as the output end of the athermal coarse wavelength division multiplexing device.
3. The athermal coarse wavelength division multiplexing device of claim 2, wherein the optical splitter is a directional coupler or a Y-splitter; the light combiner is a directional coupler or a Y-type light splitter.
4. The athermal coarse wavelength division multiplexing device of claim 1, wherein the waveguide width of the first mode waveguide is a first waveguide width, the waveguide width of the second mode waveguide is a second waveguide width, and the first waveguide width is not equal to the second waveguide width.
5. The athermal coarse wavelength division multiplexing device of claim 4, wherein the first waveguide width is 1000 nanometers and the second waveguide width is 600 nanometers.
6. The athermal coarse wavelength division multiplexing device of claim 4, wherein the first and second waveguide arms are each provided with two waveguide converters.
7. The apyrous coarse wavelength division multiplexing device according to any of claims 1 to 6, wherein the predetermined delay requirement is:
(nTE1(λ)·LTE1-nTE0(λ)·LTE0)·k0-m·2π＝delay(λ)；
the preset temperature insensitivity requirement is as follows:
(ΔnTE1(λ)·LTE1-ΔnTE0(λ)·LTE0)·k0＝0；
where λ is the wavelength in the medium, nTE1(λ) is the effective refractive index of the TE1 mode, LTE1Length of TE1 mode walk, nTE0(λ) is the effective refractive index of the TE0 mode, LTE0The length of TE0 mode, m is the interference order, delay (λ) is the time delay corresponding to wavelength λ, Δ nTE1(λ) is the effective refractive index change, Δ n, of the TE1 mode at different temperaturesTE0(lambda) isEffective refractive index change value, k, of TE0 mode at different temperatures0Is the wave vector in vacuum, k0＝2π/λ0，λ0Is the wavelength of light in vacuum.
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